It is a well-known fact that no fertilizer, of whatever composition, is ever utilized by the crop with a complete efficiency. This occurs particularly with nitrogen-based fertilizers, although it is encountered also with all water-soluble fertilizers. The main reason for this deficiency is the rapid dissolution of the fertilizer in the soil, where only a part thereof is actually utilized, the balance being lost in the draining of rain or irrigation water. Two main solutions were suggested to overcome this disadvantage:
(a) use of chemically prepared slow-release fertilizers, such as ureaform, isobutylidene diurea, oxamide etc., and
(b) use of physically prepared slow-release fertilizers, by coating the fertilizer granules with sulfur, wax or synthetic polymers, which decrease the removal of the fertilizer from the soil by rain or irrigation water.
The disadvantage of the chemically prepared slow-release fertilizers is mainly connected with their coats, since quite expensive raw materials and/or manufacturing costs are involved. Thus for instance, in case of nitrogen-based fertilizer, it was stated that using nitrogen compounds of reduced solubility is at least twice as costly as using standard soluble nitrogen fertilizers.
Whereas the present invention deals with physically prepared slow-release fertilizers, more discussion and relevant prior art references will be presented on this approach.